Method for stopping loss of circulating fluid in well bores



United States Patent 3,219,111 METHOD FOR STOPPING LOSS 0F CIRCULATING FLUID IN WELL BORES Arthur L. Armentrout, Cooper Arms, Apt. 202, 455 E. Ocean Blvd, Long Beach 2, Calif.

N0 Drawing. Continuation of application Ser. N 0. 825,155, July 6, 1959. This application Sept. 5, 1962, Ser. No. 221,451

7 Claims. (Cl. 166-29) This application is filed as a continuation of my application Serial No. 825,155, entitled, Method and Composition for Preventing or Stopping Loss of Fluid in Well Bores, filed July 6, 1959.

This invention relates to a method for stopping the loss of drilling circulating fluid in well bores.

In the course of drilling well bores with modern rotary well drilling apparatus and methods, the bore hole is normally kept filled with clean drilling circulating fluid, which fluid serves to Wash and flush the cuttings removed by the rotary bit from the bottom of the well bore from the well bore, support the well bore walls and also establish or deposit a thin, slipper cake or film on the walls of the bore. The cake or film deposited on the well bore walls serves to seal small cracks and interstices in the surrounding formation, the entrances of which are not more than .001 or .002" in size. The cake or film also establishes a bearing surface, coextensive with the well bore on which the rotary drill pipe can bear.

The various types of modern drilling fluid involve mixtures of expansible bentonite clay and fresh water, natural clay and fresh water, attapulgite clay and either fresh or salt water, oil and Water emulsions and combinations of clays, oils and water.

The particle size in modern drilling fluids is, as a general rule, from .5 to microns. As much as 5% of the particles in such fluid may run as large as 325 mesh, but no larger.

Most of the cuttings flushed from the well be the drilling fluids range from A3 to /2 in diameter, or larger, and are removed from the drilling fluid at the top of the well be means of shaker screens, centrifugal filtering devices and the like before the drilling fluid is recirculated into and through the well structure.

The fact that such fluids are continually cleaned of large particles as drilling is carried on and only clean fluid is introduced into the well bore at the bit, as it penetrates new, porous formations, only enhances the inability of the fluids to seal anything but the smallest of openings in the formation penetrated.

As long as a Well bore does not penetrate a formation that has cracks, crevices or fractures that establish openings larger than .001" to .002", the ordinary modern drilling fluid will effectively seal and there will be no appreciable loss of circulation drilling fluid.

If, on the other hand, the formation penetrated by the bore has openings much larger than .001" or .002", the modern drilling fluid will not seal the openings, but will flow into the openings and escape from the well bore into the formation.

When a well bore suffers a complete loss of circulation into highly porous formations, the level of circulation drilling fluid in the bore hole quickly drops from the surface to a point of hydraulic pressure equalization, which point may be several hundreds to several thousands of feet below the top of the well.

Accordingly, when a well bore hole is either completely or partially emptied of drilling circulation fluid, the well bore walls are deprived of the hydraulic pressure head of the column of drilling circulating fluid extending downwardly from the surface, and consequently there will be hundreds or thousands of feet of unsupported Well wall that is free to slough off and to cave into the well bore. This sloughing off or caving in will stick or freeze drill pipe that may be in the well bore or casing that may be therein and which is in the process of being installed and cemented. Another result that may occur when circulation fluid is lost in a well bore is that the gas and/ or oil sands penetrated may be under great pressure which, if the pressure is sufiicient to overcome the static head of circulating fluid remaining in the well bore, will cause a blowout.

Where casing is being installed and cemented in place or cement plugs are being installed or other cementing operations are taking place, Portland cement slurries are often employed and these slurries likewise become lost through porous or fractured formations penetrated by the well bore.

As oil and gas wells are being drilled to progressively greater depths in the earth the problem of preventing or curing lost circulation becomes increasingly difiicult largely due to the high differential in pressures encountered in the formations penetrated by deep Well bores.

Where the well bore has penetrated depleted porous oil and gas formations and the pressures therein have become largely exhausted, the differential pressures may be 10,000 p.s.i. and even greater in favor of forcing the drilling fluids or cement slurries into the porous formations.

Many methods and materials have been tried and are presently being employed in efforts to recover lost circulation in wells. To date, such attempts are at best hitand-miss propositions. The reason for this resides in the fact that the materials being used to seal and/ or plug the formations and stop the flow of fluid therethrough are fundamentally weak and such that a dependable seal cannot be obtained.

It is recognized that a structurally strong material which is unaffected by fluid, pressure and heat and which is inert to chemicals found in wells would be ideal for recovering lost circulation. To date, the only materials having such characteristics are common sands and gravels. Attempts have been made to employ such materials to recover lost circulation, but due to their high specific gravity, they have a tendency to settle out of the circulating fluid to fill the bottom of the well bores and create additional problems rather than to solve the problem of lost circulation.

Organic materials employed include such things as cotton linters, straw, tree bark, sawdust, feathers, pulverized tire casings, ground nut shells, cotton seed hulls and the like. The great disadvantage found in such materials is their tendency to soften, ferment, rot or otherwise deteriorate or be destroyed in the environments to which they are subjected when introduced into a well and their fundamental or basic structural weaknesses, that is.

Furthermore, if they do stop the loss of drilling circulation fluid from the well bore hole into porous formation, they merely form a mat on the wall of the well bore without penetrating to any great extent the cracks, crevices, fractures or fissures through which the drilling circulation fluid escapes.

Consequently, when the well drilling operations are resumed the mat is removed from the well bore wall and the loss of drilling circulation fluid resumes.

The nonorganic materials used as bridging agents for recovering lost circulation in wells have included expanded volcanic rock such as expanded vermiculite and expanded pumicite or perlite.

All manufactured expanded volcanic rocks and natural pumice, etc., are extremely light and structurally weak. Expanded vermiculite establishes a plurality of flat irregularly-shaped particles made up of a multiplicity of stacked, extremely thin, weak, frangible and readily separable flakes or scales. Perlite or pumicite consists of small, flufly, weak, irregularly shaped granules of cellular material. These particles are extremely light, soft and frangible, due to the extremely thin frangible nature of the wall structures thereof.

To the best of applicants knowledge, all forms of expandable volcanic rock, when expanded, acquire one or the other of the above types of structure and are such that they are readily compressible or compactable and are easily and rapidly reduced and broken down into powder form or the like by light pressure. Each can be reduced to powder form by crushing them with ones fingers, or fingernails.

It has been proposed to use a baked mixture of silicate of soda and ground limestone for stopping the loss of fluids into porous formations penetrated in bore holes, but this material is useless as the silicate of soda dissolves in water and the proposed mixture disintegrates in a very short time, thereby destroying any sealing or plugging that the material may have initially accomplished.

The organic and nonorganic materials referred to above are extremely irregular in shape, having thin, weak edges, corners and projections which enhance their tendency to hang up and initiate a bridge in or across an opening in a formation but which materially limit their ability to maintain such a bridge and which interfere with their ability to enter openings in a formation, interfere with their settling, matting and/or nesting with each other and which result in extremely weak and unstable masses when matted together.

Due to the inherent weakness in these materials, a matting can only be established in situations where the pressure differentials encountered in the well structure are extremely low, for example, 100 to 200 p.s.i.

Once a sealing mat or cake is established in a low pressure situation, such as referred to above, upon reestablishment of circulation and of high operating pressures and velocities in the well, such sealing mats or cakes, being only as strong as the weakest material therein, collapse and are forced out into the formation, and washed away, rendering them ineffective.

It has been found that any method of establishing a seal in a thief formation by the use of bridging materials which is slow and is such that the flow pattern through the formation is altered and varied from time to time as the particles of material bridge, release, and bridge again in a slow build-up of the sought-after sealing cake, often results in a break down of unstable formations faster than the sealing mat or cake can be established or so washes the formation that a suitable foundation for a seal cannot be obtained.

Still further, a bridging material and/or method of introducing it into a well which is slow, necessitates the loss of a large portion of costly bridging material, circulating fluid and time.

A primary object of the present invention is to provide an improved method designed to prevent or stop loss of drilling fluid, cement slurries and the like from well bores into porous or fractured formations penetrated or traversed by the well bore. To function satisfactorily for this purpose the material used should meet certain requirements, some of which are as follows:

(1) The material used must be dry and capable of being transported to the well site in small containers such as, for example, paper bags, so that it may be manually handled.

(2) The material must be capable of being easily and quickly mixed with either conventional well-drilling circulating fluids and cement slurries, to form a pumpable mixture that can be pumped down the drilling string by the conventional slush pump in batches of from a few barrels to several hundreds of barrels and followed by the regular drilling circulating fluid.

(3) The material must easily and promptly mix with modern drilling circulation fluids or cement slurries in amounts of from 1 cubic foot to 1 /2 cubic feet or more per barrel, and at the rate of from 10-20 barrels per minute, so that it can be delivered to the point of lost circulation in a matter of minutes.

(4) The blended material must be in the neighborhood of 40 to 70 pounds per cu. ft. when loose and dry, so that it will not settle out of circulation fluids, cement slurries, or water, but will remain in a stable, uniform mixture.

(5) The material must be inorganic so that it will not ferment, rot, decompose or disintegrate and must be nontoxic to humans having occasion to handle and use it with ordinary precautions.

(6) The material must be inherently strong, capable of withstanding very high hydraulic pressures at least of the order of 10,000 p.s.i. and high temperatures in the range of 1,000 F., or more, without crushing, breaking down and disintegrating under such conditions in any manner, whether in a few hours, a few days, or years.

(7) The material must be capable of readily entering cracks, crevices, fractures or fissures in earth formations and having entered the same, serve to bridge, plug, lock and seal itself in position so that the drilling circulation fluid or cement slurries can build up therein and thereon an impervious seal in the walls of the well bore to prevent further loss of fluids from the well bore into the porous formations and in conjunction with drilling fluids or cement slurries, be capable of forming an impervious and immovable meass in the cracks, crevices, fractures, fissures or porous formations back from the well walls as soon as it enters therein.

(8) The excess of material which may remain on the well bore wall or in the bore and which does not enter the cracks and crevices must be capable of being readily removed from the walls of the well bore by conventional Well bore drilling equipment when the well bore drilling operations are resumed and not disturb the seal in the formation away from the well bore face.

(9) The material must be free from sharp corners and the like and should have a sphericity roundness and hardness as hereinafter described.

(10) The material must continue to serve the purpose for which it was installed indefinitely.

It is an object and feature of my invention to provide a method of using a novel bridging sealing material to recover lost circulation in a well which establishes a fast and positive seal in a thief formation with a minimum loss and/or expenditure of bridging material, circulating fluid and time.

It is another object of this invention to provide a method and a material of the character referred to which penetrates and establishes a seal in a thief formation where it is not subject to being destroyed by tools and circulation in the well bore and where it serves to support and shore the formation and thereby prevent subsequent leaks through the formation upon relief of pressure within the formation and/or the reestablishment of high operating fluid pressures in the well.

It is an object and feature of the present invention to establish a mixture of circulating fluid and bridging material of the character referred to, in which the said bridging material is made up of predetermined volumetric portions of screened, graded sizes of granules of said material whereby the normal pattern and/ or combination of granules held in suspension and carried by the fluid is such that it will establish an immediate, substantially complete bridge and seal upon stopping of the foremost of the larger granules and upon the advancement of the next adjacent smaller granules into engagement therewith.

The material which I employ for the purpose of stopping the loss of well-drilling circulating fluids or cement slurries is a granular aggregate of expanded marine shale. It is produced from a Pliocene marine sedimentary shale that is mined from a deposit near Ventura, California. This material, when expanded by heat into granules and later cooled, is inherently strong. The granules are noninterconnected cellular bodies having a plurality of individual, hermetically-sealed cells or cavities of varying size. Each granule has a substantially impervious outer shell or skin.

The expanded shale granules have the advantage of being more or less round in their expanded condition, the granules being generally ovoid or mammilated or botryoidal in shape, ranging from .001" to .002" to 1" and larger in diameter. This material weighs from 40 pounds to 70 pounds per cu. ft., depending upon the size of the granules, the larger size Weighing the least per given volume.

The expanded marine shale granules are chemically inert to materials found in the well drilling fluids and cement slurries encountered in bore holes. The granules can therefore be likened to ovoid or mammilated or hot- Iyoidal shaped granules or ceramic material composed of many individually hermetically-sealed cellular cavities of many different sizes and shapes of great structural strength having practically an impervious outer shell or skin.

According to the convenient measure of the granular nature of particles set forth and illustrated in Stratigraphy and Sedimentation, by W. C. Krumbein and L. L. Sloss, 1950 Edition, published by W. H. Freeman and Company, page 81, this expanded marine shale has a sphericity of from .5 to .7 (avg. .6), a roundness of from .8 to .9 and a hardness of 5.5 on the Mohs Scale of Hardness.

The granule sizes range from .0021" to over 1" in diameter and will withstand hydraulic pressures of over 10,000 p.s.i. without collapsing in any manner.

The percentage of each granule size as the expanded marine shale comes from the kilns varies radically during the manufacturing operation. Therefore, it has to be screened and classified very carefully and precisely to separate the different sizes and then recombined with the correct amount of each size.

To facilitate an understanding of the present invention there is provided Chart No. 1, which identifies granular sizes by number and which granule sizes are included in various classifications. Accompanying this specification are charts designated No. 2 through No. 7. Charts Nos. 2 through 6 set forth the percentages by volume of each granule size in classifications Nos. 1 through 5, forming the ideal or preferred compositions and also illustrate two permissible alternatives in percentages by volume that may constitute these classifications.

Chart 7 is a chart which sets forth the weight per cubic foot of each granule size and the Weights per cubic foot of the several classifications of aggregates that I provide.

In accordance With the present invention, the expanded marine shale is classified as to granule size, and as illustrated in Chart No. 1, these sizes have been arbitrarily numbered from 1 to 16. Granule size 1 are those granules which pass through a U.S.S. screen #270 have a mesh size of .0021" and which will be caught in an impervious pan. Granule size No. 2 are those granules which will pass through a U.S.S. screen #140 having a mesh size of .0041" and which are caught on a U.S.S. screen #270 having a mesh size of .0021". In a like manner, granules size No. 3 consists of granules capable of passing through a U.S.S. screen size #70, the mesh size of which is .0082" and which will be caught on a U.S.S. screen #140 having a mesh size of .0041". Sizes 4 to 16, inclusive, are identified from the chart in a similar manner.

As indicated in Chart No. 1, any one of five different classifications may be used. Thus, classification No. 1

comprises granules of sizes from 1 to 8, inclusive. Classification No. 2 comprises granules of sizes from 1 to 10, inclusive. Classification No. 3 comprises granules from 1 to 12, inclusive. Classification No. 4 comprises granules from 1 to 14, inclusive, and Classification No. 5 comprises granules from 1 to 16, inclusive.

As indicated in Chart No. 2, Classification No. 1 consists of an aggregation of 8 different sizes ranging from .1875" to .0021" and the Ideal mixture or aggregate runs from 10.75% by volume of #8 to 14.25% by volume of #1.

In Chart No. 6, Classification No. 5 consists of an aggregation of 16 different sizes ranging from 1.00" to .0021" and the Ideal mixture or aggregate runs from 4.375% by volume of #16 to 8.125% by volume of #1. Some variation is permissible in any classification.

In any event, the percentages by volume should stay inside the limits as shown. For example, in Chart No. 2,- Classification No. 1, size #8 should not be less than 9% or more than 12.5% by volume and size #1 should not be more than 16% or less than 12.5 by volume.

In each Classification the increase or decrease of the volume percentage is uniform. Also, the increase or decrease of the Granule size in each consecutive size of granule is substantially uniform.

The classification selected for the treatment of a particular well bore in which circulation has been lost depends upon the suspected size of the fissures or crevices that have been traversed by the well bore. Thus, if it is suspected that the fissure or crevices are relatively small, Classification 1 may be selected. If the use of this classification does not effect a seal, a higher classification may be tried, such as Classification No. 2 or Classification No. 3. If these classifications do not effect a seal, then Classification No. 4 or No. 5 may be used. The suspected size of the fissure or crevice that is to be closed against lost circulation does not in and of itself indicate the classification selected with reference to its maximum granule size. Thus, in Classification No. 1, the maximum size of granules includes granules that are roughly in diameter. This does not indicate, however, that Classification No. 1 can only vbe used to close fissures or crevices that are in width. On the contrary, this classification can be used to close crevices or fissures of considerably greater width, such as A" or possibly When all of the granules constituting Classification No. 1 are pumped down into the well, there will, of course, be a mixture of all the granule sizes that comprise this classification. All of these granules together will tend to follow the path of the circulation fluid that is being lost or which is flowing through the crevices or fissures. A group of the largest granules constituting this classification may become lodged back in the crevice or fissure and form a primary framework retarding the flow of circulation fluid and smaller granules therethrough. Nevertheless, these larger granules that have become lodged in the fissures or crevices have voids or spaces therebetween and these voids or spaces are sufficient to pass many of the smaller sized granules. Thus, granule sizes 1, 2, 3 and 4 of this classification can probably readily pass through the voids or spaces left between the lodged granules of granule size 8. Granules of size 7, however, ordinarily cannot pass through the voids or spaces between the lodged granules of granule size 8, and consequently become lodged against the granules of granule size 8. These granules, likewise, have spaces which will ordinarily not pass granules of granule size 6 and consequently granules of that granule size become lodged against granules of granule size 7 which, in turn, are held in position by granules of granule size 8. In a similar manner, granules of consecutively smaller granule size become lodged and tend to fill the voids or interstices between previously lodged larger granules with the result that finally extremely small granules of the granule sizes of 1 and 2 form, in effect, a substantially impervious filter cake that is supported on the larger lodged granules and effectively prevents the continued escape of circulating or drilling fluid. For this reason, if one or more consecutive granule sizes are omitted from a selected classification, leakage or continued loss of circulation is very apt to occur. For example, in Classification No. 1, if granules of granule sizes 6 and 7 are omitted, the spaces between the granules of granule size 8 are not apt to become filled or choked with granules or granule sizes 1 to 5. On the contrary, granules of these granule sizes are apt to be carried by the circulation through the voids or interstices left between the lodged granules of granule size 8. Consequently, the omission of one or more consecutive granule sizes from any classification Will rarely, if ever, accomplish a satisfactory seal or even the reduction in the amount of one granule size to a negligible quantity is to be regarded as dangerous.

Laboratory tests indicate that as a general rule the granules comprising Classification No. 1 will bridge and seal a hole or crevice in the formation having a diameter of A1" although the maximum granule size in this classification is materially less than A. Similarly, the granules comprising Classification No. 2 will bridge or seal a hole having a diameter of although the largest granule comprising this classification are materially smaller. Likewise, the granules comprising Classification No. 3 will bridge a hole having a diameter of /2". Any classification will usually bridge in a hole that is 30% larger than the diameter of the largest granule size included in the classification.

It will be appreciated that the fact that the granules being of a round or ovoid, egg-shaped r kidney-shaped character, tend to facilitate their being carried by the circulating fluid to the fissures or crevices through which circulation is being lost. Furthermore, these granules on entering the fissures or crevices by reason of their rounded character, tend to roll and slide one upon the other and to fit themselves between each other to form a solid and impervious seal. In the case of expanded marine shale, the expansion of the shale by the special method of expanding causes the shale to assume this rounded shape as distinguished from sharp angular shapes of other material.

Where the granular aggregate that I provide is mixed with dry clays designed to be mixed with Water to produce drilling mud or when the aggregate is mixed with dry cement away from the drill site, I prefer to add to the dry clay or to the dry cement approximately to by weight of the clay or cement of the Ideal classified granules constituting the selected classification. Even these percentages may vary considerably and satisfactory results still be obtained.

As illustrative of the results obtainable with the composition or aggregate constituting the present invention, in one test a high pressure test unit having a bed of x /2" gravel to a depth of 12" was employed (that is gravel which will go through openings and will not go through /2 openings). 1 /2 cubic feet of granular aggregate constituting Ideal Classification No. 1 were added to each barrel of 8% or 65 pounds per cubic foot Jel-water Bentonite drilling fluid, and this mixture was pumped through the A x /2" gravel until it sealed. The pressure urging the composition through the gravel was raised to 8,000 p.s.i. and few drops of filtrate per minute were then observed to continue to come through the gravel bed. The test unit was allowed to stand 18 hours, at the end of which time the pressure was reduced to 2,000 p.s.i. The pressure was then raised to 8,000 p.s.i. where it held. After 8 hours the pressure was released and the test bed of gravel was removed. The mixture had penetrated the M" x /2" gravel for approximately 2" and was a solid and practically an impervious seal. The face of the gravel was depressed approximately /1 on account of some of the gravel having been crushed. The surplus material at the face of the gravel bed was easily removed without disturbing the seal.

In a second test, the test unit was equipped with a 12" bed of A" x /2 gravel and 1 /2 cubic feet of the granules constituting Ideal Classification No. 2 were added to the mixture with each barrel of Rosamond Lake Clay aqueous 94 pounds per cubic foot drilling fluid. This was pumped through the gravel unit until it sealed, which occurred within a few seconds. The pressure was then raised to 9,500 p.s.i. After standing for 12 hours the pressure had dropped to 4,000 p.s.i. due to the escape of a few drops of filtrate through the gravel bed. At the conclusion of the 12 hours the pressure was again pumped up to 9,500 p.s.i. where it held. The pressure was then released and the test sample recovered from the unit. The mixture had penetrated the x /2" gravel bed nearly 2" and was a solid and impervious seal. Some of the gravel had been crushed, but the face of the gravel was nearly clean and the surplus material was easily washed away from the face of the gravel bed.

In a third test the test unit was likewise equipped with a 12" bed of A x /2" gravel. To each 94 pound (l sack) of dry Portland cement was added 1 cubic foot of dry Ideal Classification No. 1. These ingredients were thoroughly mixed and 500 pounds of the mixture was added to each barrel of water and thoroughly mixed. The resultant composition was an aqueous pumpable mass weighing in the neighborhood of pounds per cubic foot. The mixture was pumped through the x /2 gravel bed in the unit until it sealed, which occurred in a few seconds. The pressure was raised to 6,000 p.s.i. where it held. Only a few drops of clear filtrate per minute came through the seal gravel bed. After 8 hours the pressure had dropped from 6,000 p.s.i. to 3,500 p.s.i. where it held. After 8 hours the pressure was released and the gravel bed removed from the unit. The mixture had penetrated the gravel bed approximately 3". The cement and mixture had set and had become a seal in the voids or interstices of the gravel bed.

Where it is suspected that the cracks, crevices, or fissures in the formation traversed by the well bore are of approximately the size of those left by a stratum of A x A2" gravel, it is preferable to mix from 1 cubic foot to 1 /2 cubic feet of Ideal Classification No. 1 with each barrel of drilling fluid or cement slurry that is being used. Then, by closing the gates on the well bore at the surface and pumping in a surplus of drilling fluid under pressure, the mixture of Ideal Classification No. 1 will be forced into the porous formation and will effect a seal. In case the interstices are a little larger than those in a %1" x /2 gravel bed, Ideal Classification No. 2 is used. Where the lost circulation while drilling is not over 10-25 barrels per hour, then 1 cubic foot to 2 cubic feet of either Ideal Classification No. 1 or 2 can be added to the circulating fluid by adding either Ideal Classification to the drilling fluid at the suction end of the conventional rig pump through an orifice that will regulate the amount being fed into the drilling fluid from a storage bin. The granules of the selected Ideal classification will be mixed with the drilling fluid while going through the rig pump and thence down the drill pipe to the bottom of the well and up the outside of the drill pipe between the drill pipe and the well walls. Wherever the mixture of drilling fluid and granules encounters an area in the well bore wall where the drilling fluid is escaping into the porous or fractured formation, the mixture will follow the circulating fluid until the cracks, crevices, fractures, etc., are bridged, plugged and sealed.

A batch or slug of from 50 to 200 barrels can be made up in advance by adding from 1 cubic foot to 2 cubic feet of either Ideal Classification No. l or Ideal Classification No. 2 to each barrel of drilling fluid or cement slurry. After thoroughly mixing, the batch or slug can then be pumped down the bore hole to the area of lost circulation. The valve gates at the top of the bore hole can then be closed and additional drilling fluid pumped in, thus forcing the batch or slug into the porous area of lost circulation.

In case the well is being drilled by cable tools, the mixture can be located at the suspected area of lost circulation by a dump bailer. Where the circulation is being lost through very large cracks or crevices, the larger Ideal classifications are used and may be introduced into the bore hole using an apparatus similar to that illustrated in my prior United States Patent No. 2,634,098, issued April 7, 1953.

It will be noted from Chart No. 1 that progressing upwardly, each granule size from 1 to 7, inclusive, is practically 100% larger than the preceding size. Size No. 1, however, is through U.S.S. screen No. 270.0021 and stops in pan. Therefore, the size of No. 1 is a mixture, anywhere from .001 to .00 Size No. 6U.S.S. screen size .065" is .0322" larger than size No. 5U.S.S. screen size .03028", so No. 6 is slightly larger than 100% of the size of No. 5. Size 7 U.S.S. screen size .125" is .060" larger than size No. 6--.065", so No. 7 is slightly smaller than 100% larger than size No. 6. From size No. 8 to size 11, inclusive, each granule size is larger than the preceding size. From size No. 12 to size No. 16, each granular size is A" larger than the preceding size.

It is to be noted that with the particular configuration and progression of granule sizes and the volumetric proportioning of the granule sizes set forth and provided by the present invention, the composition is such that it will flow with the circulating fluid carrier into the openings in the formation to a point where it bridges and becomes lodged therein and is not subject to becoming caught, snagged, or otherwise hung-up in a precarious condition in the formation or at the wall of the Well bore, that at all times, in the flow stream there exists a combination of granules of varying size which will, if urged together, establish a structurally sound stable bridge work and an impervious mass or seal.

As a result of the above, when a batch of material that I provide enters a formation and a bridge is established by one or a limited few of the larger granules, the next ad- CHART #3.CLASSIFICATION #2 PERCENT BY VOLUME Granule Equal Size Size Volumes Ideal Alt.

(percent) (percent) (percent) CHART #4.CLASSIFICATION #3 PERCENT BY VOLUME jacent, consecutively smaller granules, upstream from the Granule Equal lodged granules are immediately stopped and create a 40 gm gigg s 583 ig substantially impervious, bridged pack in the formation, without the loss of additional time, packing material and #12 8% 5M2 2% circulating fluld and without the pOSSlblllllY of those gran- 375' #11 8% Side 320 ules which have bridged being unseated by the subsequent 13 35?, g2 passage and impact of the circulating fluid and smaller 87 8% 722 6% .125" #7 8% 8M2 7% granules belng Washed thereby. #6 8% 87/12 8% Having described only a typical preferred form of my 0328 #5 9342 9% i 0164 #4 8% 9 /i2 10% invention, I do not wlsh to be lumted to the specific de- 0082 #3 8% 10142 11% tails herein set forth, but wish to reserve to myself any 83%;: if 2% 3&2 variations or modifications that may appear to those 2 Y 6 sfiilled in the art and fall within the scope of the follow- 100 ing claims.

CHART #1 Granule Size Screen Size Larger Than Screen Size Screen Size Number U.S. Number Preceding Size Opening Opening Stop Classification Number or in Inches Starting From #1 Through #16 1" t 1. 00 .875 15 w w .875 750 10 e46" 340" .3125 9 x" 46" .250 s #4 M0 .1875 I 7 #0 100 7; .125 6 #12 100% .065 5 #20 100% .0328 #1 #2 #3 #4 #5 4 #40 100% 0164 0082 3 0082 0041 2 100% 0041 0021 1 #270 100% 0021 Pan CHART #5.CLASSIFICATION #4 PERCENT BY VOLUME Granule Equal Size Size Volumes Ideal Alt.

(percent) (percent) (percent) 750 #14 7V: 3 /28 914 625 #13 7 V: 4 928 1964 500" #12 7% 4 28 2%: .375" #11 7% 1&8 3% 3125 7 /6 5 /28 4914 250 #9 7% 52s %4 .1875 #8 79: 6 /28 %4 125" #7 7% 7 %8 7%4 065 #6 73? 7 /28 %4 .0328" #5 7% 8 %s 9914 .0164" #4 7% 8 28 10%4 .0082 #3 7 9 9 %s 11964 0041 #2 7V1 9 528 12914 0021" #1 7% 1O1%8 13914 CHART #6.CLASSIFICATION #5 PERCENT BY VOLUME the volume of every other group, each granule having Krumbein indices of sphericity of about .6 and Krumbein roundness of about .8, the granules of each group of granules being of a size which will not freely migrate through the interstices established by the granules of the next larger group when the granules of the next larger group are in bridging contact with each other and with the granules of successively larger groups.

2. The method of sealing openings in the earths formation traversed by and communicating with a well bore which comprises, simultaneously introducing into the well bore a pumpable fluid and an aggregate of commingled groups of expanded marine shale classified as to size, circulating said fluid and aggregate through the bore to and thence into the openings whereby said aggregate bridges in and seals said openings, the granules of each group being substantially the same size, the volume of the granules of each group being approximately equal to the volume of every other group, each granule having Krum- Gmnule E ml bein indices of sphericity between .5 and .7, Krumbein s si e# v m roundness between .7 and .9, and a Mob hardness of (p (P l about 5.5, the granules of each group of granules being of a size which will not freely migrate through the in- #16 4-375 terstices established by the granules of the next larger .875 #15 6. 25 4. 625 3. 0 ,750" #14 (125 4,875 25 group when the granules of the next larger group are in @331; g-

ig bridging contact with each other and with the granules .375" #11 6125 51625 5: 0 of successively larger groups.

213?," fig gg 2-8 3. The method of sealing openings in the earths forma- I 6:375 1 tion traversed by and communicating with a well bore 6%? fig g 22;? 0 which comprises, simultaneously introducing into the well 10328" #5 6:25 71125 8.0 bore a pumpable fluid and an aggregate of commingled I r e I I 852%,; gig g- S-g groups or expanded marine shale classified as to size, cir- 0041" #2 0:25 7:875 9. 5 culating said fluid and aggregate through the bore to and 0021" #1 3-125 thence into the openings whereby said aggregate bridges 100 100 100 in and seals said openings, the granules of each group being substantially the same size, the volume of the CHART #7.EXPANDED INERT MARINE SHA LE Granule Screen Screen Weight Size Size Opening, Cu. Ft.

Inches %II %II #13 r/ u %II %II #10 916" "Me" 43# ab U I! %II :h d a #8 #4 1375" 57# g 5 3 5 #7 #5 125" 58# =11; O 33 #6 #12 065" 59# o 3 2 #5 #20 0328" 60# a a e #4 #40 0164 61# T5 #3 0082 64# m Having described my invention, I claim:

1. The method of sealing openings in the earths formation traversed by and communicating with a well borewhich comprises, simultaneously introducing into the well, bore a pumpable fluid and an aggregate of commingledgroups of expanded marine shale, the granules of each group being substantially the same size, the volume of granules of each group being approximately equal to the volume of every other group, each granule having Krumbein indices of sphericity between .5 and .7, Krumbein roundness between .7 and .9, and a Mob hardness of about 5.5, the group of the smallest granules containing granules of about .001 inch, the weight per cubic foot y of the aggregate, when said aggregate contains 8 groups, the granules of each group being approximately equal to the granule size of which increases uniformly from .002

inch to .187 inch, being approximately 70 pounds and being approximately 40 pounds per cubic foot when the aggregate contains 16 groups, the granule size of which increases uniformly from .002 inch to one inch, the granules of each group of granules being of a size which will not freely migrate through the interstices established by the granules of the next larger group when the granules of the next larger group are in bridging contact with each other and with the granules of successively larger groups.

4. The method of sealing openings in theearths formation traversed by and communicating with a well bore and into and through which circulating fluid introduced in the bore is free to escape, which comprises, simultaneously introducing into the well bore a pumpable fluid and an aggregate of commingled groups of expanded marine shale, classified as to size, circulating said fluid and aggregate through the bore to and thence into the openings whereby said aggregate bridges in and seals said openings, the granules of each group being substantially the same size, the volume of the granules of each group being approximately equal to the volume of every other group, each granule having Krumbein indices of sphericity of about .6 and Krumbein roundness of about .8, the granules of each group of granules being of a size which will not freely migrate through the interstices established by the granules of the next larger group when the granules of the next larger group are in bridging contact with each other and with the granules of successively larger groups, the volume of each group of granules comprising the commingled aggregate being such that the number of granules of each next smaller size of granules is suflicient to establish a complete bridge throughout the interstices established by the next larger size of granules when said next larger size of granules are in bridging contact with each other.

5. The method of sealing openings in the earths formation traversed by and communicating with a well bore and into and through which circulating fluid introduced in the bore is free to escape, which comprises, simultaneously introducing into the well bore a pumpable fluid and an aggregate of commingled groups of expanded marine shale, classified as to size, circulating said fluid and aggregate through the bore to and thence into the openings whereby said aggregate bridges in and seals said openings, the granules of each group being substantially the same size, the volume of the granules of each group being approximately equal to the volume of every other group, each granule having Krumbein indices of sphericity between .5 and .7, Krumbein roundness between .7 and .9, and a Moh hardness of about 5.5, the group of the smallest granules containing granules of about .001 inch, the group of granules comprising the largest size granules containing granules of a predetermined size which will not freely migrate through the openings to be sealed, the granules of each group of granules being of a size which will not freely migrate through the interstices established by the granules of the next larger group when the granules of the next larger group are in bridging contact with each other and with the granules of successively larger groups.

6. The method of sealing openings in the earths formation traversed by and communicating with a well bore and into and through which circulating fluid introduced in the bore is free to escape, which comprises, simultaneously introducing into the well bore a pumpable fluid and an aggregate of commingled groups of expanded marine shale, classified as to size, the group containing the smallest granules containing granules .002 inch and less in diameter, the granules of each group of larger size granules being substantially the same size, the volume of the granules of each group being approximately equal to the volume of every other group, each granule having Krumbein indices of sphericity of about .6, Krumbein roundness of about .8, and a Moh hardness of about 5.5, the group comprising the largest granules containing granules of a size which will not freely migrate through and will bridge in the openings to be sealed, the granules of each group of smaller size granules being of a size which will not freely migrate through and will bridge in the interstices established by the next larger size granules when in bridging contact with each other, the volume of each group of granules comprising the commingled aggregate being such that a number of granules of each next smaller size of granules is sufiicient to establish a substantially complete bridge throughout the interstices established by the next larger size of granules when said next larger size of granules are in bridging contact with each other.

7. The method of sealing openings in the earths formation traversed by and communicating with a well bore and into and through which circulating fluid introduced in the bore is free to escape, which comprises, simultaneously introducing into the well bore a pumpable fluid and an aggregate of commingled groups of expanded marine shale, classified as to size, the group containing the smallest granules containing granules .002 inch and less in diameter, the granules of each group of larger size granules being substantially the same size, the volume of the granules of each group being approximately equal to the volume of every other group, each granule having Krumbein indices of sphericity of about .6, Krumbein indices of sphericity of about .6, Krumbein roundness of about .8, and a Moh hardness of about 5.5, the group comprising the largest granules containing granules of a size which will not freely migrate through and will bridge in the openings to be sealed, the granules of each group of smaller size granules being of a size which will not freely migrate through and will bridge in the interstices established by the next larger size granules when in bridging contact with each other, the volume of each group of granules comprising the commingled aggregate being such that a number of granules of each next smaller size of granules is suflicient to establish a substantially complete bridge throughout the interstices established by the next larger size of granules when said next larger size of granules are in bridging contact with each other, while an aggregate comprising 8 groups progressing uniformly in granule size from about .001 inch to about .18 inch, weighing approximately pounds per cubic foot while an aggregate comprising 16 groups progressing uniformly in granule size from about .001 inch to about one inch weighing approximately 40 pounds per cubic foot.

References Cited by the Examiner UNITED STATES PATENTS 2,561,075 7/ 1951 Sidwell 2528.5 2,634,098 4/ 1953 Armentrout 166-32 2,650,195 8/1953 Cardwell et al. 16632 2,683,690 7/1954 Armentrout 210-500 2,788,323 4/1957 Brakel et al. 2528.5 2,815,079 12/1957 Goins 16629 2,846,390 8/1958 Lummus et a1 16633 2,943,680 7/1960 Scott 16621 BENJAMIN HERSH, Primary Examiner.

CHARLES E. OCONNELL, Examiner. 

1. THE METHOD OF SEALING OPENINGS IN THE EARTH''S FORMATION TRAVERSED BY AND COMMUNICATING WITH A WELL BORE WHICH COMPRISES, SIMULTANEOUSLY INTRODUCING INTO THE WELL BORE A PUMPABLE FLUID AND AN AGGREGATE OF COMMINGLED GROUPS OF EXPANDED MARINE SHALE, THE GRANULES OF EACH GROUP BEING SUBSTANTIALLY THE SAME SIZE, THE VOLUME OF THE GRANULES OF EACH GROUP BEING APPROXIMATELY EQUAL TO THE VOLUME OF EVERY OTHER GROUP, EACH GRANULE HAVING KRUMBEIN INDICES OF SPHERICITY OF ABOUT .6 AND KRUMBEIN ROUNDNESS OF ABOUT .8, THE GRANULES OF EACH GROUP OF GRANULES BEING OF A SIZE WHICH WILL NOT FREELY MIGRATE THROUGH THE INTERSTICES ESTABLISHED BY THE GRANULES OF THE NEXT LARGER GROUP WHEN THE GRANULES OF THE NEXT LARGER GROUP ARE IN BRIDGING CONTACT WITH EACH OTHER AND WITH THE GRANULES OF SUCCESSIVELY LARGER GROUPS. 